Fungal pretreatment parameters for improving methane generation from anaerobic digestion of corn silage.

Corn silage was treated by white rot fungi (WRF) to investigate the effect of pretreatment on material's ability to produce methane in anaerobic digestion (AD). The selective fungi Pleurotus ostreatus and Dichomitus squalens promoted biogas generation, whereas the non-selective Trametes versicolor and Irpex lacteus had negative effect. Cumulative methane production after 10-day pretreatment with P. ostreatus at 28 °C rose 1.55-fold. The longer pretreatments of 30 and 60-days had smaller effect. When the pretreatment with P. ostreatus was carried out at 40 °C a high H2S release affected the AD process. Effect of WRF action dependent on the type of corn silage. With typical corn silage, the lignin depolymerisation raised the methane generation from 0.301 to 0.465 m3kgVS-1. In contrast, extensive decomposition of hemicellulose in hybrid corn silage deteriorated the effect of pretreatment on methane production.

Dry anaerobic digestion of the fine particle fraction of mechanically-sorted organic fraction of municipal solid waste in laboratory and pilot reactor.

High-solid anaerobic digestion of the very small particle fraction of mechanically-sorted organic fraction of municipal solid waste (OFMSW) was examined in mesophilic digestion tests in a conventional laboratory (0.013 m3) and a pilot (0.300 m3) reactor. The non-biodegradable and recalcitrant molecules together with the low protein and starch contents of the small-particles of OFMSW limited the methane generation potential of substrate. In the conventional AD system, methane yields remained low at 0.139 m3kgVS-1 due to formation of a non-reacting layer on digestate surface, which restricted utilization of the available in OFMSW digestible organics. The absence of surface solid crust in the pilot unit favoured consumption of a greater proportion of volatile solids of the OFMSW. Dry AD was remarkably stable over the entire period and negligibly effected by the toxic H2S yields. Methane generation (0.167 m3kgVS-1) was increased 1.2-fold compared to the conventional system due to a better mixing of substrate and microorganisms achieved inside the pilot reactor, which led to an increase of the digested volatile organics. Digestate presented low stability and high heavy metal content, both of which restrain its implementation as soil conditioner or fertilizer in agriculture. A secondary co-digestion treatment may be required for the neutralization of digestate.

Two-stage psychrophilic anaerobic digestion of food waste: Comparison to conventional single-stage mesophilic process.

Food waste collected exclusively from University restaurant was tested under anaerobic digestion (AD) conditions to determine its biomethane generation potential. The digestion characteristics of food waste were evaluated in BMP tests and in a conventional single-stage mesophilic CST Reactor. The suitability of psychrophilic two-stage AD to convert food waste was investigated by using a novel two-stage psychrophilic semi-continuous reactor, consisted of a vertically-oriented cylindrical reactor and a coaxially incorporated vertical tube able to spatially separate acidification from methanogenesis. Food waste presented significant methane generation performance under mesophilic conditions. Relatively high amounts of H2S released during process evolution did not have a significant effect on biogas production. For psychrophilic two-stage AD, H2S generated during start-up provoked reactor's instability only for a few days. The system was stable and operated at steady-state conditions over the course of the main AD. Higher amount of biogas was produced by the two-stage psychrophilic reactor (0.800 m3 kgVS-1) than the mesophilic single-stage system (0.751 m3 kgVS-1). However, the average methane quantities generated by the two systems were remarkably similar (0.444 and 0.440 m3 kgVS-1). Psychrophilic process was more efficient in utilizing higher proportions of volatile organics contained in substrate for methane generation than mesophilic operation. The low-temperature two-stage reactor was more energy-efficient than the mesophilic CSTR for digestion of food waste. Two-stage anaerobic digestion system operating under psychrophilic conditions might be an economically feasible option for efficiently digesting food waste.

Assessment of high-solid mesophilic and thermophilic anaerobic digestion of mechanically-separated municipal solid waste.

Mechanically-sorted organic fraction of municipal solid waste (OFMSW) was tested to determine its biogas and biomethane generation efficiency. Methane production capability of OFMSW was examined in biochemical methane potential (BMP) tests. The factors affecting the high-solid anaerobic digestion (AD) of feedstock were investigated in a series of long-term semi-continuous digestion tests performed at dry mesophilic and thermophilic conditions in a continuously rotating drum reactor with working volume of 0.013 m3. OFMSW presented low biogas and methane generation capacity due to its contained non-biodegradable components and the low proteins and starch proportions. Dry mesophilic AD allowed only a relatively limited fraction of OFMSW volatile solids to be consumed for biogas and methane production. Reducing particle size favoured utilization of higher proportions of the available digestible organic substances, and concurrently promoted biogas and biomethane generation rate. Stability of methane generation was also significantly improved by particle downsizing. Small particles compensated the limited mass transfer and restricted distribution of methane production intermediate metabolites caused by water absence in the dry AD system. Dry thermophilic AD converted sufficient quantity of OFMSWs biodegradable content. The average methane released from dry thermophilic AD (0.176 m3kgVS-1) was higher than that of dry mesophilic AD of fine particles (0.148 m3kgVS-1) and much higher than that of dry mesophilic AD of same grain size (0.114 m3kgVS-1). High temperature proved more suitable for anaerobically digesting mechanically-sorted OFMSW.

Cultivation and characterization of Cynara Cardunculus for solid biofuels production in the Mediterranean region.

Technical specifications of solid biofuels are continuously improved towards the development and promotion of their market. Efforts in the Greek market are limited, mainly due to the climate particularity of the region, which hinders the growth of suitable biofuels. Taking also into account the increased oil prices and the high inputs required to grow most annual crops in Greece, cardoon (Cynara cardunculus L.) is now considered the most important and promising sources for solid biofuel production in Greece in the immediate future. The reason is that cardoon is a perennial crop of Mediterranean origin, well adapted to the xerothermic conditions of southern Europe, which can be utilized particularly for solid biofuel production. This is due to its minimum production cost, as this perennial weed may perform high biomass productivity on most soils with modest or without any inputs of irrigation and agrochemicals. Within this framework, the present research work is focused on the planning and analysis of different land use scenarios involving this specific energy crop and the combustion behaviour characterization for the solid products. Such land use scenarios are based on quantitative estimates of the crop'sproduction potential under specific soil-climatic conditions as well as the inputs required for its realization in comparison to existing conventional crops. Concerning its decomposition behaviour, devolatilisation and char combustion tests were performed in a non-isothermal thermogravimetric analyser (TA Q600). A kinetic analysis was applied and accrued results were compared with data already available for other lignocellulosic materials. The thermogravimetric analysis showed that the decomposition process of cardoon follows the degradation of other lignocellulosic fuels, meeting high burnout rates. This research work concludes that Cynara cardunculus, under certain circumstances, can be used as a solid biofuel of acceptable quality.